Thank you very much, patch applied!
Now that you've dived into (ice-9 format), what about this one: (format #t "~,,2f~%" 0.01) => 1.0 (format #t "~,,3f~%" 0.01) ; !! => 010.0 (format #t "~,,3f~%" 0.001) => 1.0 (format #t "~,,4f~%" 0.001) ; !! => 0010.0 (format #t "~,,4f~%" 0.0001) => 1.0 (format #t "~,,5f~%" 0.0001) ; ok somehow... => 10.0 regards > On 18 Oct 2021, at 23:22, Timothy Sample <samp...@ngyro.com> wrote: > > Hi Guilers, > > It turns out there’s a little blunder in ‘format’ (from ‘ice-9’). Look > at what happens when using the SCALE argument to format a fixed-point > float (this is Guile from the Git repo at the time of writing): > > GNU Guile 3.0.7.6-22120 > Copyright (C) 1995-2021 Free Software Foundation, Inc. > > Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'. > This program is free software, and you are welcome to redistribute it > under certain conditions; type `,show c' for details. > > Enter `,help' for help. > scheme@(guile-user)> (format #t "~,,3f~%" 0.00123) > 0.23 > $3 = #t > scheme@(guile-user)> (format #t "~,,1f~%" 0.00123) > ice-9/boot-9.scm:1685:16: In procedure raise-exception: > Value out of range 0 to 400: -1 > > Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue. > > The first example gives the wrong result. Scaling 0.00123 by 3 should > yield 1.23, not 0.23. For the second example, instead of 0.0123, we get > an error! What’s going on here? > > Well, our ‘format’ code comes from SLIB and was written in 1998, so it’s > not easy to explain. There’s so much mutation even a C programmer would > blush! ;) The issue happens in the ‘format:parse-float’ procedure > (which is defined inside of ‘format’). It normalizes the string > representation of a number, and applies the scale argument when needed. > It does this by keeping a string of digits and the location of the > decimal point. Another thing it keeps track of the leading zeros in a > variable called ‘left-zeros’. Here’s the code that does the final > shifting and places the decimal point: > > (if (> left-zeros 0) > (if (<= left-zeros shift) ; shift always > 0 here > (format:fn-shiftleft shift) ; shift out 0s > (begin > (format:fn-shiftleft left-zeros) > (set! format:fn-dot (- shift left-zeros)))) > (set! format:fn-dot (+ format:fn-dot shift))) > > The issue is that the cases in the inner ‘if’ form are reversed. That > is, if there are MORE leading zeros than we need to shift, we can just > shift. Otherwise (if there are FEWER leading zeros), we need to shift > out the zeros and then move the decimal point (‘format:fn-dot’). > > AFAICS, this bug was in the original SLIB implementation (1998) and has > not been fixed since then. It’s been in Guile since 1999. > > Anyway, that’s more than anyone cares to know.... Here’s a patch with > tests! :) > > From c31d1f5d44343da1201ea1be86bc6b2ac8af6c8d Mon Sep 17 00:00:00 2001 > From: Timothy Sample <samp...@ngyro.com> > Date: Mon, 18 Oct 2021 17:07:41 -0400 > Subject: [PATCH] ice-9 format: Fix scaling floats with leading zeros > > --- > module/ice-9/format.scm | 4 ++-- > test-suite/tests/format.test | 10 ++++++++-- > 2 files changed, 10 insertions(+), 4 deletions(-) > > diff --git a/module/ice-9/format.scm b/module/ice-9/format.scm > index 48d9c0c84..ee7cba910 100644 > --- a/module/ice-9/format.scm > +++ b/module/ice-9/format.scm > @@ -1359,10 +1359,10 @@ > (else > (if (> left-zeros 0) > (if (<= left-zeros shift) ; shift always > 0 here > - (format:fn-shiftleft shift) ; shift out 0s > (begin > (format:fn-shiftleft left-zeros) > - (set! format:fn-dot (- shift left-zeros)))) > + (set! format:fn-dot (- shift left-zeros))) > + (format:fn-shiftleft shift)) ; shift out 0s > (set! format:fn-dot (+ format:fn-dot shift)))))))) > > (let ((negexp ; expon format m.nnnEee > diff --git a/test-suite/tests/format.test b/test-suite/tests/format.test > index b9aa7a854..d5111f1c6 100644 > --- a/test-suite/tests/format.test > +++ b/test-suite/tests/format.test > @@ -2,7 +2,7 @@ > ;;;; Matthias Koeppe <mkoe...@mail.math.uni-magdeburg.de> --- June 2001 > ;;;; > ;;;; Copyright (C) 2001, 2003, 2004, 2006, 2010, 2011, 2012, > -;;;; 2014, 2017 Free Software Foundation, Inc. > +;;;; 2014, 2017, 2021 Free Software Foundation, Inc. > ;;;; > ;;;; This library is free software; you can redistribute it and/or > ;;;; modify it under the terms of the GNU Lesser General Public > @@ -121,7 +121,13 @@ > ;; in guile prior to 1.6.9 and 1.8.1, leading zeros were incorrectly > ;; stripped, moving the decimal point and giving "25.0" here > (pass-if "string 02.5" > - (string=? "2.5" (format #f "~f" "02.5")))) > + (string=? "2.5" (format #f "~f" "02.5"))) > + > + (pass-if "scale with few leading zeros" > + (string=? "1.23" (format #f "~,,3f" "0.00123"))) > + > + (pass-if "scale with many leading zeros" > + (string=? "0.0123" (format #f "~,,1f" "0.00123")))) > > ;;; > ;;; ~h > -- > 2.33.0 >
